The present invention generally relates to recording and reproducing of a PCM audio signal, and more particularly to a method and an apparatus for recording and reproducing a coded audio signal, either alone or together with a video signal, to and from a magnetic tape by a rotary magnetic head type scanner, and still more particularly to a method and an apparatus for recording and reproducing a PCM audio signal which are suitable for use when the sampling frequency for the PCM audio signal and the rotation frequency of the scanner are asynchronous.
The recording and reproducing of the PCM audio signal have been adopted in order to improve the quality of the audio signal accompanied with video.
For example, an 8 mm video recorder might utilize an audio PCM system. The sampling frequency of the audio PCM signal is two times as high as the repetition frequency of the horizontal synchronization signal. It is different from an internationally common sampling frequencies (32 kHz, 44.1 kHz or 48 kHz). For example, the sampling frequency of an audio PCM signal in a satellite broadcast is 32 kHz or 48 kHz.
On the other hand, in a MUSE system, which is one transmission systems for a high grade television system, the sampling frequency of the audio PCM signal is 32 kHz or 48 kHz. Thus, if data sampled at the above sampling frequency are to be recorded field by field, the number of data per field includes a fraction. In order to resolve this problem, a packet transmission system having a leap field to absorb the excess has been adopted, as disclosed in NHK Technical Journal 27-7, page 282.
In a video disk, the PCM audio signal is recorded at the sampling frequency of 44.1 kHz with the same format as that of a compact disk.
However, when the PCM signal is to be recorded by an apparatus such as a video tape recorder which records or transmits the signal discontinuously in time, the following problems arise. First, when the field frequency of the video signal is not an integral multiple of the sampling frequency of the audio signal, the problem described above is encountered in coding. While a solution such as the MUSE system described above has been proposed, there must be a synchronous relationship between the field frequency fv of the video signal, or the rotation frequency f.sub.D of the head scanner which rotates synchronously with the field frequency, and the sampling frequency f.sub.s of the video signal. This imposes a limitation on the system application range.
As an apparatus for PCM recording and reproducing only the audio signal by a rotary head type VTR, a consumer PCM encoder/decoder (registered in September 1983) of the Japanese Electronic Industries Association Technical Standard CPZ-105 is known. A recording and reproducing apparatus in accordance with the above Technical Standard is disclosed in the article "Digital Audio/Video Combination Recorder Using Custom Made LSI's, IC's" presented at the 69th Convention, 1981 May 12-15, Los Angles AES 1791 (B-6), particularly FIGS. 1 and 14. In this article, in the NTSC system, the field frequency f.sub.v and the sampling frequency f.sub.s are divided from the same master clock and they have a relationship of f.sub.s =735 f.sub.v. Accordingly, the number of samples per field is constant at 735.
FIG. 1 of the above article shows a block diagram of one configuration of an apparatus for recording and reproducing sampled PCM signals. An address in a RAM, which serves as an interleaving memory, is controlled by an address control circuit.
However, when the PCM audio signal is to be recorded together with a video signal by a rotary head helical scan type VTR, if the video signal is a 525 lines/60 fields television signal, the field frequency (f.sub.v =59.94 Hz) is not an integral multiple of the sampling frequency (f.sub.s =32 kHz, 48 kHz), and the number of blocks per field includes a fraction.
As a result, a block set, which is an aggregation of a predetermined number of blocks for processing the signal, such as by interleaving and deinterleaving, is separated between the fields, and this is inconvenient.
A rotary head type digital audio type recorder (R-DAT) for recording only the audio signal is known, and a portion of its specification has been published in "Technical Standard of Rotary Head System (R-DAT)", Dempa Shimbun, Oct. 7, 1985, page 48.
In each of the above cases, it is assumed that the field frequency f.sub.v and the sampling frequency f.sub.s have a certain relationship and there is no discussion of the case where f.sub.v and f.sub.s are not correlated.
In the prior art techniques described above, the sampling frequency of the video signal is not the internationally common sampling frequency, the number of quantized bits is small, and the sampling frequency of the audio signal and the field frequency have a synchronized relationship. Thus, when a video signal from a camera and a digital signal from a compact disk are to be recorded together, it is very difficult to simultaneously record them because the sampling frequencies are different and there is no synchronous relationship between the sampling frequency and the field frequency.
A solution to the above problem has been proposed in British Patent Application No. 423452 filed on Sept. 17, 1984 (JP-A-61-73207). Since it has not been published before the present invention, it is not cited herein as prior art.